1. Field of the Invention
The present invention relates to an electron-emitting device and a production method thereof and, more particularly, to an electron-emitting device having a lower electrode, an insulating layer having pores, and an upper electrode stacked in this order on a substrate, and a method for producing the electron-emitting device.
2. Related Background Art
The conventionally known electron-emitting devices are generally classified under two kinds, thermionic emission devices and cold cathode emission devices. The cold cathode emission devices include field emission type (FE type) devices, metal/insulator/metal type (MIN type) devices, surface conduction electron-emitting devices, and so on.
The FE type devices are disclosed, for example, in W. P. Dyke and W. W. Dolan, xe2x80x9cField emission,xe2x80x9d Advance in Electron Physics, 8, 89 (1956) or in C. A. Spindt, xe2x80x9cPHYSICAL Properties of thin-film field emission cathodes with molybdenum cones,xe2x80x9d J. Appl. Phys., 47, 5248 (1976).
The tip of an electron-emitting body of the field emission type electron-emitting devices is one called a cone having the three-dimensionally sharp-pointed shape and an electron beam is emitted from the tip of the cone by placing a strong electric field between a gate electrode with an aperture, disposed above the cone, and an electron-emitting region.
In order to overcome the problem in the production method of the above field emission devices, which is the need for complicated steps and expensive apparatus for forming a recessed portion for formation of the electron-emitting region, Japanese Laid-open Patent Applications No. 5-298252 and No. 5-211029 describe examples in which holes of an anodic oxide film of aluminum are used as apertures of the gate electrode and in which electron-emitting regions are formed in the holes of the anodic oxide film. These conventional examples will be described referring to FIGS. 32 and 33.
FIG. 32 is a sectional view of the electron-emitting device in Japanese Laid-open Patent Application No. 5-198252. FIG. 33 is a sectional view of the electron-emitting device in Japanese Laid-open Patent Application No. 5-211029. In FIG. 32, reference numeral 161 designates an insulating substrate, 162 an electroconductive layer, 163 an insulating film, 164 through holes, 165 the gate electrode, and 166 cathodes. The insulating film 163 is the anodic oxide film of aluminum and the tip of the cathodes 166 is of the cone shape similar to that of the electron-emitting body of the field emission devices. In FIG. 33, reference numeral 171 designates a metal layer, 172 the Al anodic oxide film, 172a micropores, and 173 cylindrical electrodes. The application describes that in FIG. 33 the distance can be made constant between the cylindrical electrodes 173 and the gate electrode or between the needlelike electrodes and the anode electrode, so as to make electron emission efficiency constant.
The MIM type devices are disclosed, for example, in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devices,xe2x80x9d J. Appl. Phys., 32, 646 (1961).
Recent researches on the MIM type are seen in Toshiaki Kusunoki, xe2x80x9cFluctuation-free electron emission from non-formed metal-insulator-metal (MIM) cathodes fabricated by low current anodic oxidation,xe2x80x9d Jpn. J. Appl. Phys. vol. 32 (1993) pp L1695, Mutsumi Suzuki et al., xe2x80x9cAn MIM cathode array for cathode luminescent displays,xe2x80x9d IDW ""96 (1996) p529, and so on.
An MIM type electron-emitting device according to Kusunoki or Suzuki et al. described above will be described referring to FIG. 34. FIG. 34 is a schematic sectional view of the MIM type electron-emitting device. In the same figure, reference numeral 1 denotes a substrate, 2 a lower electrode, 3 an insulating layer, and 4 an upper electrode. The electron-emitting device is made by a production method for first forming SiO2 on the Si substrate by sputtering, depositing Al as the lower electrode, further forming an anodic oxide film of high quality in the thickness of 5.5 nm while controlling oxidation rates, using ethylene glycol and tartaric acid, and thereafter forming Au of the upper electrode in the thickness of 9 nm. It is described that good electron emission characteristics were achieved by applying voltage between the anode of the upper electrode and the cathode of the lower electrode thus formed. Specifically, according to Kusunoki et al., negative resistance does not appear in the device current flowing against the voltage applied to the device. The xe2x80x9cnegative resistancexe2x80x9d herein is a phenomenon in which the device current decreases as the device voltage increases. In addition, fluctuation does not occur in the emission current. Here, the xe2x80x9cfluctuationxe2x80x9d means temporal change of the emission current. It is also described that dependence of the emission current on the device voltage varies depending upon the thickness of the insulating layer and that the thicker the insulating layer, the higher the device voltage that has to be applied. It is further described that with anodic oxide films made at high oxidation rates, the negative resistance appears in the electron emission characteristics and the fluctuation occurs large.
An example of the surface conduction electron-emitting device with improved electron emission characteristics is described in Japanese Laid-open Patent Application No. 9-82214. This will be described referring to FIGS. 35A and 35B. In the figures, reference numeral 191 denotes a substrate, 192 an electron-emitting region, 193 an electroconductive film, 194 a cathode device electrode, 195 an anode device electrode, 196 a fissure, and 197 a field correcting electrode. In the surface conduction electron-emitting device of this example, electrons emitted move in an electric field established by the cathode and the anode and a singular point of the electric field above the anode device electrode affects the ratio of electrons reaching the anode electrode, provided to sandwich a vacuum with the electron emitting element i.e., the electron emission efficiency. This device is an example in which the field correcting electrode is provided outside the device electrodes in order to improve the electron emission efficiency.
According to the studies by Spindt et al., the conventional FE type electron-emitting devices, however, had a problem of a spread of the electron beam, which was hindrance against enhancement of definition. In the example of application of the holes of the anodic oxide film to the apertures of the gate electrode, there remained a problem of poor repeatability in formation of the cone of the electron-emitting region. In the example in which the electron-emitting regions were formed in the cylindrical shape, there also arose problems of poor repeatability of the electron emission characteristics and high driving voltage. In the surface conduction electron-emitting device provided with the correcting electrode, the electron emission efficiency was increased, but the potential of the correcting electrode was high, which was a problem in driving.
In the conventional MIM type electron-emitting devices, first, the thickness of the insulating layer was thin, several nm, and the thickness greatly affected the electron emission characteristics. In an electron source equipped with many devices, variations in the thickness of the insulating layer are directly bound to variations in the emission current, so that control of variations is difficult. When an image pickup device or an image forming device is constructed using the electron source; there will arise a problem of degradation of image quality. Second, the quality of the insulating layer did not affect only the electron emission characteristics, but also affected the device current. In the case of the electron source equipped with many devices, variations in the quality of the insulating layer are directly bound to variations in the emission current. Particularly, in the case of a large area, control of variations is difficult. In the image pickup device or the image forming device using the electron source, there will arise the problem of degradation of image quality. Third, repeatability was poor as to occurrence of the negative resistance and occurrence of the fluctuation of the device current and control thereof was difficult.
In the conventional surface conduction electron-emitting device provided with the correcting electrode, the electron emission efficiency was increased, but the potential of the correcting electrode was high, which was the problem in driving.
An object of the present invention is thus to provide an electron-emitting device having stable electron emission characteristics with less variation that can achieve high electron emission efficiency, high definition, and low driving voltage.
For accomplishing the above object, the present invention provides an electron-emitting device comprising a lower electrode, an insulating layer having a pore, and an upper electrode stacked in this order on a substrate, wherein a carbon deposit is provided in the pore.
The present invention also provides an electron-emitting device comprising a lower electrode, an insulating layer having a pore, and an upper electrode stacked in this order on a substrate, wherein an electron-emitting region is provided in the pore, the electron-emitting region is comprised of a small gap between the lower electrode and the upper electrode, and the small gap is formed by a rim-shape electroconductive body formed along an inner wall of the pore, and the upper electrode.
The present invention further provides an electron-emitting device comprising a lower electrode, an insulating layer having a pore, and an upper electrode stacked in this order on a substrate, wherein an electron-emitting body is provided in the pore, and where when a thickness of the upper electrode is t, a length of the pore is L, and a mean free path of electron transmission of the upper electrode is xcex, they satisfy the following condition: 0.5xc3x97Lxe2x89xa6t less than 2xcex.
The present invention also provides an electron-emitting device having a lower electrode, an insulating layer having a pore, and an upper electrode stacked in this order on a substrate, the electron-emitting device having an electron-emitting region in the pore, wherein the electron-emitting region is comprised of a small gap between the lower electrode and the upper electrode and wherein a distance from the small gap to a top surface of the upper electrode is not more than 200 nm.
The present invention further provides a production method for producing an electron-emitting device comprising a lower electrode, an insulating layer having a pore, and an upper electrode stacked in this order on a substrate, the electron-emitting device having a carbon deposit in the pore, the production method comprising a step of forming the lower electrode of a metal or a semiconductor on the substrate, a step of forming an anodic oxide layer on a surface of the lower electrode, a step of producing the carbon deposit in the pore of the anodic oxide layer by applying a voltage under existence of an organic material, and a step of forming the upper electrode.
The present invention further provides a production method for producing an electron-emitting device comprising a lower electrode, an insulating layer having a pore, and an upper electrode stacked in this order on a substrate, the electron-emitting device having a carbon deposit in the pore, the production method comprising a step of forming the lower electrode of a metal or a semiconductor on the substrate, a step of forming an anodic oxide layer on a surface of the lower electrode, a step of forming the upper electrode on the lower electrode after formation of the anodic oxide layer, and a step of producing a carbon deposit in the pore of the anodic oxide layer by applying a voltage to the upper electrode and the lower electrode under existence of an organic material.
In the electron-emitting devices of the present invention, the holes are formed in the porous structure in the insulating layer such as the oxide film formed by anodic oxidation, at least the carbon deposit being the electron-emitting body is formed in the holes of the porous structure, and the gap is provided between the lower electrode and the upper electrode; therefore, with application of the voltage between the lower electrode and the upper electrode so as to keep the upper electrode at a higher potential, the electrons injected from the lower electrode tunnel through the gap between the carbon, formed on the lower electrode, and the upper electrode into a vacuum, whereby the electrons are emitted.